It is well know that many polymers can be exothermically produced as powders in fluid bed reactors wherein the fluidization is provided by a circulating mixture of gases that includes the monomers. It is known that the fluidizing gases leaving the reactor can be recirculated with cooling before reintroduction to the reactor in order to remove the heat of reaction and keep the fluid bed temperature near a desired temperature. Further, it is known that a portion of the recirculating stream may be condensed in coolers (heat exchangers) before re-insertion into the reactor. It is advantageous to remove the latent heat of vaporization, in addition to the sensible heat accumulated in the gas, since the latent heat of vaporization may be much larger per degree of cooling than the sensible heat of the uncondensed stream.
A variety of methods are used for reintroduction of the cooled recycle gas and liquids to the reactor. Often, most of the cooled recycle gas is injected into the reactor through a distributor plate below the fluid bed. The condensed recycle liquids may be entrained in the recycle gas or injected directly into the bed through some sort of nozzle assembly. Examples of the above technologies are shown in U.S. Pat. Nos. 3,595,840, 4,543,399, 4,588,790, 5,352,749, and International Publication WO 94/28032.
A compressor is used to continuously suction the fluidizing gas up out of the reactor so that it can travel through a cooling unit prior to being reinserted into the bottom of the reactor. Int. Pub. WO 94/28032 discloses the efficiencies of condensing a portion of the gas stream and removing the liquid produced therefrom prior to compression of the remaining gaseous recycle stream. Noting that the compressor action adds an additional amount of heat to the recycle stream, Int. Pub. WO 94/28032 further discloses an advantage in cooling the recycle gas again after compression to remove the heat of compression.
Since the rate of fluid bed polymer production is limited by the temperature inside of the fluid bed reactor, the rate of polymer production can be increased as more cooling is provided to the reactor. In light of the above, it would be desirable to provide a continuous fluid bed polymerization process including a method for withdrawing a higher amount of heat from the fluid recycle stream.